Intent to prototype: math-depth property and font-size: math

Summary: Implements the math-depth and font-size: math properties which indicate how deep some part of a mathematical formula with respect to the top-level `` and that a scale has to apply to font-size. This is used by MathML to implement automatic scaling in scripts etc, as well as for the scriptl

Intent to deprecate: MathML scriptminsize and scriptsizemultiplier attributes

In bug 1548471, I intend to deprecate the MathML scriptminsize and scriptsizemultiplier attributes. These are used to let people provide custom style for a minimal font-size when doing scriptlevel changes or a scale factor to apply to font-size at each scriptlevel change. The MathML Refresh CG agr

happy bmo push day!

the following changes have been pushed to bugzilla.mozilla.org: (tag: https://github.com/mozilla-bteam/bmo/tree/release-20200928.1) https://bugzil.la/1665916 : Remove block severity from blocklist bug creation template https://bugzil.la/1665891 : Overlaid image viewer is not full in height http